Buck and Hen Salmon: How to distinguish sex.

Sexing Salmon:  Bucks and Hens.

How to tell male from female salmon and steelhead.

Last year, 2009, the Oregon Department of Fish and wildlife considered the option of allowing anglers to harvest (retain, kill) only male Chinook, and if I remember correctly, there would also have been a size slot within which harvest would have been allowed.  The purpose of the proposed regulation was to allow some fishing, and some harvest, of male salmon in a certain age class.

When the dust settled, the proposal was not adopted.  ODFW biologists believed that the proposal had some biological merit, but were unsure whether anglers would be able to accurately distinguish between male and female kings.  Then too, the State Police expressed concern regarding their officer’s ability to monitor compliance, conduct education with anglers, and enforce this regulation, if it had been adopted.

Personally, I found the proposal most intriguing.  I appreciated the proposal’s biological basis, and also understood the social and administrative challenges that adoption of the regulation would have created.

Bottom line – this regulation, or something like it, could become a normal part of our angling future. A continuation of poor ocean survival conditions,  vastly fluctuating survival between brood years, a general decline in the freshwater capacity of our rivers, or even social pressures, could change the landscape for salmon anglers.

Think it sounds silly to contemplate a bucks-only harvest restriction on king salmon?  Isn’t there more social than biological basis for hunting regulations that target bucks?  Not a wildlife biologist, so this is dangerous territory for me to dabble.

I simply want to make the point that our regulation landscape, and our value-based thinking about harvesting salmon could evolve in the future.  The day could dawn when our opportunity to fish at all depends on releasing hens.

For now, let’s just talk about the next time one of us is lucky enough to catch an actual salmon or steelhead.  What should we look at to decide if it is male or female, buck or hen?

Here is a short list of the body characteristics I look for to decide if I am looking at a buck or a hen.  Head shape; relative head size; body cross-section; adipose fin size; jaw shape; my, how sharp your teeth are; the presence or absence of distended vent; and body color.

All of these morphological traits are useful to distinguish male from female salmon, and to a less dramatic extent, to distinguish male and female steelhead also.  My remarks and the photos I will show are principally limited to Chinook and steelhead.  Some of us anglers take it that an understanding of distinguishing between male and female salmon is simple.  To many anglers, though, it is not.

First thing to note is that the differences between males and females becomes much more obvious as salmon approach sexual maturity.  Recognizing sex differences in immature ocean salmon is more difficult, and I have little personal experience (like none) so I won’t talk about this situation.  Suffice to say that it is far more complicated to distinguish both species and sex of immature salmon in the ocean.

As salmon approach sexual maturity, however, the difference between species – and between bucks and hens – becomes far more obvious.  In Pink salmon, the males develop a great hump (hence Humpie) but the females do not.  In Chum salmon, bucks develop a huge hooked jaw with fang-like teeth, but the hens do not.  These extreme morphological changes are directly associated, we think, with mating rituals, fighting among males for dominant status to spawn with a specific female.

Here is pretty much what  a male Sockeye looks near sexual maturity.

The striking physical differences between each salmon species probably helps the species recognize their own, and helps minimize hybridization – although there are many other factors like olfaction (sense of small), body size, spawning season, homing, and spawning habitat selection – that all contribute to the salmon’s ability to maintain their species’ distinction.

Blah blah.  Sorry.

Head shape. Buck Chinook salmon have a convex sloped forehead; hens have a convex sloped head.  This is the case for steelhead also, although the differences we see in steelhead are usually not quite as dramatic as they are in king salmon.

The Chinook above is a hen.  The Chinook below is a buck.

Relative head size. This can be subtle, but bucks have larger heads than hens, when one looks at similar sized fish.

Body cross-section. Bucks tend to be laterally compressed, hens tend to be round.  This means that a buck will be narrower and taller – a hen will tend to be rounder and shorter for fish of similar weight.  A view of a maturing buck from above, or head-on, helps one see these differences more clearly and the differences increase as the buck salmon becomes more mature.

Adipose fin size. Wish I had a good photo to show this distinguishing feature.  Suffice to say, bucks have much larger adipose fins than hens.  Big bucks have huge adipose fins and they can be 2-3 times larger than the adipose fin on a similar weight hen.

Jaw shape. Make king salmon develop a hooked nose –a kype – and the teeth of bucks grow larger than the teeth of hens.  King salmon do not develop kypes as dramatic as do, for example, Coho salmon, Atlantic salmon, or Chum salmon – but the kype of buck Chinook is noticeable; females do not develop kypes.

Fangs. Male king salmon exhibit larger teeth than hens.  Male king salmon do not develop fangs as dramatically as do male Chum salmon, but development of long, foreboding teeth on the males of both species is noticeable.  Female Chinook to not develop fangs like the males.

Check out the fangs on the male chum salmon pictured above.  My, grandma, what big teeth you have.  This male also shows the developing kype of the jaw, a characteristic you would not see on the female.

A distended vent on ripening females. As female salmon and steelhead become more sexually mature, as they ripen, their vent begins to protrude slightly.

Body color. Male king salmon develop a distinctive copper-bronze hue as they approach maturity.  Hen Chinook can be fully mature and still appear to be fairly “bright.”  These fish are not really what we would consider “chrome”, they just have not become dramatically colored as the males. Buck Sockeye and Coho salmon develop much brighter body hues than do Chinook bucks.  Point is, the bucks sport the most dramatic colors on the spawning grounds.

Here is the body color of a male Chinook, above, the bonze hue I mention.  Note also that the adipose fin is big and the vent is not distended.

Here is a mature Chinook female. Note that this hen does not have the “bronze color” of a male at a similar stage of maturation, could be mistaken as a bright fish, (had fresh sea lice), but has a well distended vent.

Hope these notes and photos help.

Steelhead?  The morphological differentiation between male and female steelhead are not as drastic as the differences displayed by Chinook, Chum, Pink, coho, and Sockeye salmon, even though all are classified as Pacific salmon.  Below, check out the head shape of a bright male (first photo) and female (second photo).  Both of these steelhead are hatchery fish.

Finally, here are three sketches. The first, of a pair of kings as seen from above;  the buck is the slimmer of the two fish.  The next sketch is a classic male Chinook – large head, concave slope of the forehead, no distension of the vent, and large adipose fin.  The final sketch s a female Chinook salmon approaching maturity – smaller head, rounded forehead, small adipose fin, and a slightly protruding vent.

We are fortunate to share the salmon’s rivers.


8 thoughts on “Buck and Hen Salmon: How to distinguish sex.

  1. Great job! Am forwarding a copy of this to my grandson…he can out fish me, but now I just showed him something that he didn’t know.


  2. very illuminating, Jay. I recently killed a chrome bright hatchery fish for the BBQ at the end of a great day drifting down the river with my wife, catching several on the swing.

    Was surprised when what I had been convinced was a male turned out to be a female with a very immature egg sac.

    As one who occasionally harvests a male fish if the run seems plentiful, this “show and tell” should be helpful with a more accurate ID…

  3. I’ve been fooled by late-season hens (chinook) which can develop a lesser kype and big teeth. Some of these kypes are quite prominent. But the distended ovipositor is a dead giveaway, along with the bulging egg sacks showing through paper-thin rib-walls.

  4. In the first part, you use the word convex to describe both bucks and hens. Then later you use the word concave to describe the heads of the males.

    1. My bad. Bucks have a concave shape to the head, hens are convex. I had to look it up just now to be sure. Thank you! JN

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